A carbureter for internal combustion engine structurally features that a by-pass air inlet channel is arranged on the mixer cavity body of mechanical carburetter. The air inlet of said by-pass air inlet channel is connected with an air filter. The outlet of said by-pass air inlet channel has two branch pipes, one being connected via horizontal gas channel to by-pass secondary idle regulating hole and another via the hole on throttle axle to the by-pass gas channel for regulating secondary gas supplement for whole working condition. A regulation valve of total by-pass gas is arranged to the by-pass air inlet channel. Its advantages are full combustion, high thermal efficiency and power of engine, low oil consumption and less environmental pollution. |